The present invention relates to an improved self-scanning photodiode array. In the prior art, such an array comprises a plurality of photodiodes arranged in a row. The array is moved in a forward horizontal direction while the outputs of the photodiodes are sequentially scanned to produce output signals. This operation is performed many times during the forward movement of the array to scan a rectangular area of an original document for electrostatic copying, facsimile transmission or the like. The array is inclined relative to the forward scan direction rather than perpendicular thereto by an angle depending on the geometry of the array and the speed of movement thereof so that the output signals represent points on the document which lie on a straight vertical line. After this operation is completed, the document is moved by a distance equal to the height of the array for indexing and the array is returned in a reverse horizontal direction to its home position. Then, the operation is repeated to scan an adjacent rectangular area of the document.
In this prior art arrangement, no scanning is performed during the reverse or return movement of the array and this time is effectively wasted. Although the scanning operation could be performed during the reverse movement, it would result in a distorted reproduction due to the inclination of the array. Means for reversing the inclination of the array for scanning in the reverse direction may be provided, but would constitute an excessively complicated mechanical arrangement.